System for reducing powertrain reaction torque

ABSTRACT

A system is provided for controlling the inertia of a vehicle&#39;s powertrain during sudden braking events. Torque generated by rapid deceleration of the vehicle&#39;s drive wheels during braking is prevented from being transmitted through the vehicle&#39;s driveline by a clutch which disengages the drive wheels from high effective inertia components in the driveline. The clutch is actuated by a signal produced by any of several sensors on the vehicle which sense a sudden braking event. Driveline speed is adjusted to match drive wheel speed before the clutch is deactivated to reengage driveline with the drive wheels.

FIELD OF THE INVENTION

This invention generally relates to vehicle powertrains, and deals moreparticularly with a system for controlling powertrains having highinertias and reaction torques.

BACKGROUND OF THE INVENTION

Environmental concerns and the need for fuel conservation has spurredthe development of new hybrid propulsion systems for vehicles. Hybridelectric vehicle (HEV) powertrains for example, typically includeelectric traction motors, high voltage electric energy storage systems,and modified transmissions. Electric energy storage systems includebatteries and ultra capacitors. Primary power units for these systemsmay include spark ignition engines, compression ignition directinjection (e.g., diesel) engines, gas turbines and fuel cells.

HEV powertrains are typically arranged in series, parallel orparallel-series configurations. With parallel-series arrangements,multiple motors operating in multiple operating modes sometimes requirethe use of several gear sets to effectively transmit power to thetraction wheels. As a result, HEV powertrains often possess considerableeffective inertia at the wheels compared to conventional ICEpowertrains. This is due in part to the potentially large inertia of thehybrid motor devices, as well as the significant gearing from motor towheels that is often employed.

Powertrains possessing relatively high effective inertias such as thoseof HEVs, result in certain problems that require solutions. For example,the application of braking force to the vehicle's traction wheels duringa sudden braking event, may result in a very rapid angular momentumchange in the powertrain. Specifically, a rapid deceleration of thetraction wheels during braking results in a counter-torque beingtransmitted from the traction wheels back through the driveline. Becausemany of the components connected in the driveline have relatively largeeffective inertias at the wheels, the counter-torque produced by thebraking event can produce relatively high reactive torque levels in thepowertrain. This reaction torque is transmitted through the gearingmechanisms to the transmission housing, and can have deleterious effectson powertrain and driveline components, particularly under suddenconditions, such as when the vehicle's ABS system is activated.

Accordingly, a need exists in the art for a system of reducing orcontrolling powertrain inertia during operating conditions that imposehigh inertial forces on drive train components. The present invention isintended to satisfy this need.

SUMMARY OF THE INVENTION

A system is provided for controlling inertial forces within a vehiclepowertrain during certain operating conditions, such as sudden brakingevents. The control system reduces these inertial forces through the useof relatively simple powertrain components such as clutches and existingvehicle sensors. A further advantage of the present system resides inits compatibility with a wide range of HEV configurations and powertraingeometries.

In accordance with a first, non-limiting embodiment of the invention, amethod is provided for controlling a vehicle powertrain during a brakingevent, which includes at least partially disengaging the powertrain froma set of traction wheels when the onset of the braking event is sensed.The braking event is sensed using a variety of methods, includingmonitoring the vehicle's existing ABS (Antilock Braking System), ormeasuring the rotational speed of the traction wheels. In oneembodiment, a planetary gear in the transmission is controlled in amanner to disconnect the driveline from the traction wheels. In anotherembodiment, an automatically actuated clutch is used to disconnect thepowertrain from the wheels. In still another embodiment, a slip clutchis used to partially disconnect the powertrain from the traction wheels,thereby reducing the counter-torque applied to the driveline by thetraction wheels.

According to another non-limiting aspect of the invention, a hybridvehicle drive system is provided that includes an internal combustionengine, an electric motor, a pair of vehicle traction wheels and adriveline connecting the traction wheels with the combination of theinternal combustion engine and the electric drive motor. The system alsoincludes a vehicle braking system for applying brake force to thetraction wheels during a braking event, and an inertial control systemfor controlling the effective powertrain inertia at the wheels during avehicle braking event. The inertial control system is automaticallyactivated by control signals produced during a braking event. The systemincludes one or more devices which partially or fully disengage thedriveline from the wheels vehicle before undesirable counter-torqueproduced by the rapidly decelerating wheels is transferred back throughthe driveline.

These and other features and advantages of the present invention may bebetter understood by considering the following details of a descriptionof a preferred embodiment of the invention, which should be consideredas illustrative and non-limiting. In the course of this description,reference will frequently be made to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a combined block and diagrammatic view of a powertrain for ahybrid electric vehicle, employing an inertial control system inaccordance with one embodiment of the present invention;

FIG. 2 is a block diagram showing additional details of the presentinvention;

FIG. 3 is flowchart showing the steps employed in carrying out anexemplary control method of the present invention;

FIG. 4 is a block diagram of a generic architecture for a hybrid vehiclesystem; and,

FIGS. 5A–5C are block diagrams showing exemplary hybrid powertrainsystem configurations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 4 shows a generic architecture for a hybrid vehicle system 134, towhich the present invention may be applied. The system 134 includes aprimary power source 114, such as a gasoline, diesel or other gas fuelsupply, coupled to a primary power generating system 116, such as aninternal combustion engine. The primary power generating system 116generates a primary drive torque that is transmitted to the vehicle'sdriveline 132 via power transmission assembly 118. The powertransmission assembly 118 can be a conventional manual, automatic orcontinuously variable automotive transmission, or other equivalentgearing mechanism for transmitting mechanical power produced by theprimary power generating system 116. The system 134 further includes asecondary power source 120, such as a battery, ultracapacitor, hydraulicaccumulator or other energy storage device, and secondary powergenerating system 122, such as one or more electric machines or othertorque generating devices, for supplementing the drive torque deliveredby the primary power generating system 116. The system may furtherinclude an auxiliary power source 126 coupled to an auxiliary powergenerating system 128, such as a fuel cell system or Auxiliary PowerUnit (APU) for providing additional drive torque.

The primary power generating system 116 may, for example, be a gasoline,natural gas, hydrogen or other gaseous, fuel-burning internal combustionengine. Power transmission assembly 118 transmits the output of both theinternal combustion engine 116 and the secondary power generating system122 to the vehicle driveline 132. The power transmission assembly 118may be a converter-less automatic transmission constructed and arrangedwith the secondary power generating system 122, such as an integratedhigh voltage electric motor/generator. The power transmission assembly118 and secondary generating system 120 can be packaged into a singlemodular hybrid transmission unit 124

FIGS. 5A through 5C show exemplary hybrid powertrain systemconfigurations that may be used to implement the present invention. Thesystems shown in FIGS. 5A-5C are shown by way of example and notlimitation.

FIG. 5A depicts a so-called “series” hybrid configuration 136 having aninternal combustion engine 142 coupled to a modular hybrid transmissionunit 144. Modular hybrid transmission unit 144 includes an electricgenerator 154 that produces electrical energy for powering the vehicledrive wheels 150 via an electric motor 156 and gear set 158. Electricalstorage device 152 stores electrical energy via the generator 154 whenthe internal combustion engine produces more power than required, andsupplements engine power via the electric motor when power demandexceeds the engine power output. FIG. 5B show a so-called “parallel”hybrid configuration 138 wherein modular hybrid transmission unit 46delivers driveline torque via a first power path having the internalcombustion engine 142, a coupling device 160 and a gear set 162. Thecoupling devices 160, can be any suitable devices, for example a gearset or clutch, for transmitting mechanical energy to the vehicledriveline 160. The coupling devices 160, 166 can be the same device.FIG. 5C shows a so-called “parallel-series” configuration 140 wherein amodular hybrid transmission unit 148 includes motor/generators 172, 174electrically and/or mechanically coupled, for example via planetarygearset, to deliver power to a gearset 170 and driveline 150.

Referring now to FIG. 1, a high effective inertia powertrain 74 fordriving a vehicle is depicted. In the illustrated embodiment, thepowertrain 74 is suitable for use in an HEV utilizing one or more fueland/or motor drives. As shown, the powertrain 74 includes an internalcombustion engine (ICE) 10 and a DC electric motor 54, each connectedthrough a later-described driveline to drive a pair of traction wheels68, sometimes also referred to as drive wheels. The engine 10 has acrankshaft 12 rotating in the direction of arrow 14, which is connectedto the driveline by a damper coupling 16. The rotating friction of theengine 10 is schematically indicated by the damper 40. Torque istransmitted by the damper coupling 16 through a rigid or compliant shaft20 to a planetary gear set 22. A damper 18 between the damper coupling16 and the shaft 20 functions to isolate torsional fluctuationstransmitted from the engine 10 to the transmission line. The planetarygear set 22 includes a carrier gear 24 and sun gear 26 driving a ringgear 28. A one-way clutch 30 connected between the carrier gear 24 and atransaxle housing 42 functions to prevent the engine 10 from rotating ina reverse direction. The transaxle housing 42 encases transmission anddifferential components. The mechanical mounting or connection of thesevarious components is schematically represented by the various brokenlines 92 connecting these components to transaxle housing and engineblock 42. The sun gear 26 is connected through an output shaft 32 of anelectric motor generator 36 whose speed is controlled by a torquecontrol signal delivered to its control input 38.

Although not specifically shown, it should be noted that the motor 54and generator 36 are connected with one or more suitable energy storagesystems. The speed of the carrier gear 24 and the engine 10 is afunction of the speeds of the ring gear 28 and the sun gear 26. Thus,generator 36 is used to control the speed of the engine 10 by changingthe speed of the sun gear 26. The use of the generator 36 to control thespeed of the engine 10 may be used in an intelligent control system tocontrol engine speed independent of driveline speed. A clutch 34operated by a control signal at its input 52 functions to selectivelylock the generator 36 against rotation. Locking the generator 36prevents the sun gear 26 from rotating, the result of which is theplanetary gear 22 directly connects the engine 10 to the traction wheels68.

Ring gear 28 is connected through counter shaft 48 and gear assemblies50, 64 to a torque splitting device in the form of a differential 66. Aparking brake 44 actuated by control signal at its input 46 is connectedto and selectively locks the countershaft 48 against rotation. Gearassemblies 50, 64 possess inertia represented by the numeral 62. Thedifferential 66 splits the driveline torque and delivers it through apair of half shafts 88, 90 respectively to the traction wheels 68.

A second power source for driving traction wheels 68 is provided by theDC electric motor 54 whose speed is determined by a torque controlsignal received at its input 56. Motor 54 provides the dual function ofdriving the traction wheels 68 and acting as a regenerative brakinggenerator. During vehicle braking, the motor 54 functions as anelectrical generator using kinetic energy of the vehicle to generateelectricity that is stored in a battery (not shown) for later use. Themotor 54 delivers torque at its output shaft 58 through a gear set 60 tothe differential 66, which in turn transmits the torque to the tractionwheels 68. The motor 54 possesses a relatively high effective inertia atthe wheels, compared to an conventional ICE powered vehicle, due in partto its own inertia as well as that of the gear assemblies 60 and 64.

The powertrain 74 described above possesses a relatively high amount ofeffective rotating inertia at the wheels, compared to the powertrain ofa conventional ICE powered vehicle. This relatively high amount ofeffective rotating inertia is partially due to the use of multiple drivemotors, motor controls and gear sets that are necessary to manage thedelivery of power to the traction wheels 68. A major portion of thisinertia is attributable to the electric motor 54 and the gear sets 60and 64 that mechanically connect it to the traction wheels 68. The gearsets 22 and 50 also materially contribute to the effective powertraininertia, as does the ICE 10 and the generator 36. The various componentparts of the powertrain 74 are mechanically connected either directly orindirectly to a transaxle housing and ICE engine block 42. The transaxlehousing and engine block 42 are in turn carried on correspondingtransaxle and engine block mounts 70 that are secured to the vehicle'schassis 108. Thus, numerous components, including gear assembliestransmit torque to mountings on the transaxle housing and engine block42, which in turn transfer this torque to the mounts 70.

In the event of a sudden braking event, as occurs during a sudden wherethe vehicle's ABS system is actuated, the braking force applied to thetraction wheels 68 causes rapid deceleration of these wheels, in turnresulting in a rapid deceleration of the powertrain that is mechanicallyconnected to the wheels 68. This rapid deceleration of the powertrain,which has a large effective inertia, produces a commensurately largecounter-torque which is transferred back through the driveline andpowertrain 74. This counter-torque is transmitted to each of thepowertrain components where it is applied to the transaxle housing andengine block 42, and their mounts 70. The reactive forces on thetransaxle housing and engine block 42, as well as their chassis mounts70 are particularly high because of the large effective rotating inertiaof the powertrain 74. As a result, the reactive forces applied to thetransaxle housing and block 42, and the mounts 70 may be sufficient todamage these components under certain sudden braking conditions. Evenunder normal braking conditions the relatively high powertrain inertiaand torque levels can produce undesirable noise, vibration and harshness(NVH). Furthermore, large fluctuating torques in the powertrain canaffect the performance of the ABS system.

In accordance with the present invention rapid changes in powertrainangular momentum stemming from sudden braking is controlled by limitingor substantially eliminating the amount of reactive torque transmittedbetween the traction wheels 68 and the powertrain components upstreamfrom the wheels, particularly those contributing higher effectiverotational inertias. As will be described below, this inertial controlcan be carried out by either completely disconnecting high inertiapowertrain components from the wheels 68, in response to a brakingevent, or by reducing the amount of reactive torque transmitted throughthe driveline during a braking. The inertial control of the presentinvention may be implemented using one or more clutches 72 forselectively disengaging high inertial components of the powertrain 74.For example, a clutch 72 may be interposed between gear sets 60 and 64to disengage the electric motor 54 from the differential 66.Alternatively, a clutch 72 may be interposed between gear sets 50 and 64to disengage both the electric motor 54 and engine 10. In order toeffect even greater control over powertrain inertia, one or two clutches72 may be installed between the differential 66 and the traction wheels68, thereby allowing disengagement of the entire powertrain 74 from thetraction wheels 68.

Referring now also to FIG. 2, the construction of the clutch 72 willdepend on the particular application and available packaging geometries,however a number of conventional mechanisms can be employed to providethe clutch function. For example, a conventional clutch disc assemblymay be employed in which a number of friction disc plates are broughtinto engagement with each other to connect an input shaft with an outputshaft. In one approach, the clutch discs are normally biased intoengagement with each other to connect the input shaft with the outputshaft, and a control signal is used to actuate a hydraulic or electricalactuator which forces the discs apart in the event of a braking event.Alternatively, hydraulic pressure may be employed to normally force theclutch plates together which are spring biased to separate whenhydraulic pressure is removed in response to a braking signal.

A number of other clutch and similar technologies may be employed suchas an integrated wheel end, a magnetorheological or electroheologicaldevice. In any event, the clutch 72 is automatically actuated by asignal generated by a controller 76 which may be a dedicated, programmeddevice, or an existing controller on the vehicle which is used to managethe inertial control system as an auxiliary function. Essentially, thecontrol signal received by the clutch 72 is indicative of an brakingevent in which the level of brake force applied to the traction wheels68 is sufficient to create undesired levels of counter-torque in thepowertrain 74. The controller 76 actuates the clutch 72 in response toany of a variety of signals or vehicle conditions that indicate anaggressive or sudden braking event. Examples of such signals are thoseproduced by the vehicle's existing ABS sensors 78, brake pedal braketravel sensors 80 or various event prediction sensors 82 used to predictevents or conditions suggesting that sudden braking may be required orimminent. In addition, the inertial control system may rely on its owndedicated event sensors 84 which might comprise by way of example,inertial sensors or body deflection sensors which senses eventssuggesting that sudden braking is eminent or has commenced. Similarly,torque sensors 86 mounted on the transaxle housing or engine block 42,or their mounts 70 could be used to sense when an unusually highreactive torque is present in the powertrain 74 which requiresactivation of a clutch 72 to disengage the powertrain 74 from the wheels68. In any event, it is important that the various sensors or othersignal generators used to activate the clutch 72 have a particularlyrapid response time so that the powertrain is disengaged beforesignificant reactive torque can be transmitted.

Although a clutch 72 has been described and illustrated as a suitablemeans of disengaging the power train, other equivalent devices aresuitable for effecting powertrain disengagement and reactive torquecontrol. For example, a device can be provided for locking the ring gear28 against rotation in response to a braking event. Such a device would,in effect, function very similar to the parking brake 34, preventing thereactive torque in the powertrain 74 from reaching the engine 10.Alternatively, any one of the gear sets 50, 60, 64 could be replaced bya planetary gear assembly that would nominally have one port (ring, sunor carrier) locked against the transmission housing. When the powertrainis to be disconnected, the locked port would be released and allowed tospin freely, thereby disconnecting the powertrain from the wheels.

In many cases, it may be desirable to reconnect the driveline andpowertrain 74 with the wheels immediately following a braking/powertraindisconnect sequence. For example, when a vehicle passes over a series ofice patches, the vehicle's ABS system may be successively activated forbrief periods, resulting, each time in the powertrain being disconnectedfrom the wheels. If however, during the period of disconnection, thedriveline speed falls substantially below that of the wheels, thereconnection process may produce substantial NVH, and in some cases,possibly damage the driveline components. Therefore, in accordance withthe present invention, the driveline speed is synchronized with that ofthe wheels before they are reconnected. This is achieved by sensing boththe driveline and wheel speeds using corresponding sensors 110, 112, anddetermining the speed difference using the controller 76. Based on thedetermined speed difference, the controller transmits a control signalto any of the motor 54, generator 36 or the engine 10 to increasedriveline speed until it is within a preselected range of the wheelspeed, at which time the controller 76 deactuates the clutch 72 therebyeffecting re-engagement.

Attention is now also directed to FIG. 3 which shows the basic stepsemployed in carrying out the control method of the invention. Brake andother systems on the vehicle are monitored at step 94 to determinewhether an aggressive or sudden braking event has occurred, is about tocommence, or could potentially occur in the immediate future. Aspreviously discussed, this monitoring function can be performed by any avariety of sensors on the vehicle which feed information to a controller76. At step 96, the controller 76 determines whether an aggressive orsudden braking event has occurred, based on the information developed bythe event sensors. If it is determined that a sudden braking event isoccurring, the controller 76 actuates the clutch 72 to disengage thepowertrain 74, as indicated at step 98. In order to assure smoothreengagement of the powertrain 74 with the wheels 68 at the end of thebraking event, the controller continues to monitor the informationprovided by the event sensors to determine when the sudden braking eventhas ended, as shown at step 100. When it is determined that the brakingevent has ended, the powertrain speed is adjusted at step 102, so thatthe powertrain speed is close to the speed of the wheels 68. Next, atstep 104, a determination is made of whether the powertrain speed iswithin certain limits that assure smooth re-engagement. If thepowertrain speed is within these limits, then at step 106, the clutch isactuated to re-engage the powertrain 74 with the wheels 68

It is to be understood that the specific methods and techniques whichhave been described are merely illustrative of one application of theprinciple of the invention. Numerous modifications may be made to themethod as described without departing from the true spirit and scope ofthe invention.

1. A method of controlling reaction torque transmitted through a highinertia vehicle powertrain during a rapid vehicle braking event,comprising the steps of: detecting a rapid braking event in which abrake force is applied to at least one vehicle drive wheel producesreaction torque that is transmitted from the drive wheel through thehigh inertia powertrain; and, reducing upstream of the drive wheel inthe powertrain, the reaction torque produced by the applied brake forcewhen a rapid braking event is detected.
 2. The method of claim 1,wherein the detecting step comprises sensing an application of one ormore vehicle brakes.
 3. The method of claim 1, wherein the detectingstep comprises sensing a speed of the drive wheel.
 4. The method ofclaim 1, wherein the detecting step comprises sensing an operatingcondition of the vehicle indicating that a rapid braking event will beinitiated.
 5. The method of claim 1, wherein the detecting stepcomprises sensing when an automatic braking system on the vehicle isactuated.
 6. The method of claim 1, wherein the detecting step comprisessensing the application of a preselected level of torque to at least onecomponent of the powertrain during the braking event.
 7. The method ofclaim 1, wherein the reducing step comprises disconnecting the drivewheel from the powertrain.
 8. The method of claim 1, wherein thedetecting step comprises sensing an operating condition of the vehicleindicating a rapid deceleration of the drive wheel.
 9. The method ofclaim 1, wherein the reducing step comprises actuating a clutch.
 10. Themethod of claim 9, wherein actuating the clutch comprises allowing theclutch to slip such that only part of the torque applied to thepowertrain by the drive wheel is reduced.
 11. The method of claim 9,wherein actuating the clutch comprises disconnecting the drive wheelfrom the powertrain.
 12. The method of 9, wherein actuating the clutchcomprises disconnecting the drive wheel from a portion of thepowertrain.
 13. The method of claim 7, further comprising the step ofreconnecting the drive wheel to the powertrain after the braking eventis ended.
 14. The method of 13, wherein reconnecting the drive wheelcomprises: comparing a speed of the drive wheel with a speed of thepowertrain, adjusting the speed of the powertrain to a preselected rangebased in part on the drive wheel speed.